Friday, May 22, 2015

Study of evoked potentials | Diseases and conditions: Medical tests.

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What is a study of evoked potentials

The study of evoked potentials is a test that is used to study the brain electrical activity from external stimuli. Each of these stimuli is collected by a different sensory organ, which are translated into electrical impulses that travel through the neurons to specific areas of the brain where they are interpreted. This study records the electrical activity through a series of surface electrodes that pick up electrical impulses and extend them to study them. It is therefore a very similar to electroencephalogram test.
Thanks to these studies it is possible to identify neurological lesions in almost any area of the nervous system; In addition, they are particularly useful in patients who, for various reasons, can not express if you are able to notice external stimuli.
Evoked potentials studies are divided according to the sensory organ that is studied. The main ones are:
Study of Visual evoked potentials: studies the brain reception of Visual stimuli. To do so are asked to the person subjected to the study to look at a screen showing a flashing white light.
Study of somatosensory evoked potential: explores the brain receiving tactile stimuli. This placed a series of electrodes on the skin areas that want to study and apply mild electric shocks.
Study of auditory evoked potentials: explores the brain receiving auditory stimuli. This produced a series of clicks and treble tones that are audible to the human ear.
The doctor who analyzes such tests is the neurophysiologist or neurologist. The study is usually performed on units specific Neuropsychological what's in hospitals and clinics, and with data that contribution will be an analysis of the origin of the neurological alterations that the patient has. It is not a very expensive test, but their interpretation is difficult, and must always be accompanied by a good full medical study using clinical interview and physical examination.

When doing a study of evoked potentials

Evoked potentials studies are useful when the following diseases are suspected:
Screening of deafness in infants: with these studies can be checked that a newborn receives auditory stimuli in the brain, discarding so you have a damage in the ear.
Identification of neural lesions: almost any disruption in the nerve pathways could be detected using this type of studies. It is often used for this reason in the diagnosis of multiple sclerosis, polytraumatized or spinal cord paralysis, among other disorders.
Discard simulations or psychiatric pathology: there are certain situations in which neurological symptoms are simulated voluntarily or in the context of a psychiatric disorder. The study of evoked potentials is a completely objective test that detects if really electrical signals reach the brain.
Diagnostic tumor acoustic nerve neurinoma: this type of tumor appears in the nerves that transmit nerve impulses from the ear to the brain. It causes deafness and can be detected through these studies.
Study of the patient in a coma: when a person is in a coma, it is difficult to say which parts of the brain are danadoas. Evoked potentials identify brain areas that have no activity despite the external stimuli.
Study of blindness: evoked potentials can be noted if the nerve injury that prevents the vision is found in the retina and the optic nerve, or if you are in the cerebral cortex responsible for receiving electrical signals.

Preparation for the study of evoked potentials

If they are going to carry out a study of evoked potentials , these are issues that you must take into account:
Duration: the study of evoked potentials lasts 1-2 hours, although much of this time is dedicated to the preparation and collection of the necessary material.
Income: this study can be performed in a hospital with a unit of neurophysiology, without the need for income. After the test you can go back to your normal life. They recommend you have slept little last night, except if it is a test of Visual evoked potentials, in which case you should arrive well rested.
Is necessary to be accompanied?: is not necessary to be accompanied.
Drugs: don't need to take any prior medication. Must be communicated to the doctor all the medicines taken regularly, and will decide which suspend or maintain, especially if you take drugs for epilepsy, muscle relaxing, antiarrhythmic, or psychiatric diseases.
Food: no need to remain in fasting prior to testing or after.
Clothes: you can go to the quote from the test with the same clothes every day; Perhaps they will call you discover you the part of the body to study. Avoid creams and products of personal hygiene in the area of the body to study. You should also avoid wear masks or lacquers in the hair.
Documents: it is important to take with you the steering wheel which shows the performance of this test. You have to carry the health insurance card and medical history on diseases to study, if you have them, although the doctor will already have it with him. It can give you a document after the test.
Pregnancy and breast-feeding: evoked potentials studies are not contraindicated in pregnancy or lactation.
Contraindications: may be a type of study that are contraindicated in patients with epilepsy because certain (especially Visual) stimuli can trigger a crisis. Not tend to make tactile stimuli to persons with myopathies or other diseases of the muscles, by the risk of that sustained spasms.

How the study of evoked potentials

To make a study of evoked potentials, first the doctor will assess if it is useful for the diagnosis. If you see fit, I will quote you one day for the test and you will explain the basic measures that you need to know to submit yourself to it. Avoid drinks with caffeine (coffee, Coca Cola, energy drinks, etc.) the day before the test, and you don't put creams or lotions the day of the test in the area of the body that go you to study, nor lacquer, masks or hair gel on the hair. If it's a Visual evoked potentials test ask you that you rest well in house to be awake and alert for the next day, but for the rest they will ask you you to stay within hours, because thus you'll be more drowsy and it will be easier to perform the test.
When you arrive at the hospital and passes to the test room ask you to lean on a bed or a comfortable armchair. If it is necessary to ask you that you discover the part of your body to study. They cleaned the surface of the skin and hair with antiseptic products to remove germs and remove surface fat. The electrodes placed them you glued to the skin with a gel; also use a gel on the scalp, but the electrodes are usually put assemblies in a CAP to make installation easier. If it's a somatosensory study may put you electrodes on legs, arms and back.
The number of electrodes is highly variable, depending on the neurological study alteration, sensory organ affected, and extension of the study. It varies from a couple of electrodes to more than twenty. All electrodes have a cable that terminates in an oscilloscope that records all the electrical signals.
Once placed all electrodes is to stimulate in various ways, depending on the sensory to study organ. If it is a study of Visual potentials you'll see repeated flashes of light, moving chess boards, and other forms of light. If it is an aural study you will hear clicks and treble repeatedly. If it is a somatosensory study, you will notice small little annoying, electrical discharges in areas of skin that have to study. During that time the technician who is performing the test will give you simple commands, like that you close your eyes or you breathe deeply.
Once the test completes one electrode will be one. You should be cleaned again the area to remove the gel, but then at home you will have to clean you better and wash your hair. You can then make your daily normal activities, although keep in mind that your hair can offer an aspect of poor hygiene.

Complications of the study of evoked potentials

The study of evoked potentials is a very little invasive test and does not usually pose any risk for people who perform it. Some complications have been described is that some of the electrodes can irritate skin in especially sensitive people, something very rare.
The study of Visual evoked potentials should be performed with caution in people who have suffered previous seizures.

Results of the study of evoked potentials

Throughout the study of evoked potentials the different electrodes pick up electrical signals, which are stored in a digital memory. At the same time that the test you can see these measurements, but it is virtually impossible to analyze them because it takes time and dedication to study different records at the same time.
The neurophysiologist will analyze the registry of nerve impulses that have been detected in each of the studied nerve regions. A series of waves, which are altered according to the intensity and duration of the neuronal signals shall be respected in each record. They must study carefully to verify that indeed the electrical alterations are due to external sensory stimuli.
You can go to collect the results to the doctor who sent you the test, and which will normally be a neurologist or ENT. In that quote professional explain the alterations that have been throughout the study. It may necessary to perform more tests requiring more diagnosis, such as a CT scan or an MRI. It will explain the various treatment options in your case, and will recommend you the most appropriate.
Published for educational purposes
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